Hitherto, in a CMOS image sensor, each pixel includes, not only a photodiode (PD) that photoelectrically converts incident light, but also transistors including a transistor (TG) that transfers an electric signal which is obtained by photoelectric conversion, a reset transistor (RST), an amplification transistor (AMP), and so forth, and a floating diffusion (FD) unit. When light leaks into these active regions, photoelectric conversion occurs. A false signal is generated by electrons that are produced as a result of the photoelectric conversion, and is regarded as noise. Accordingly, generally, the regions are blocked from light in the CMOS image sensor in order to prevent light from entering the regions. Additionally, wiring lines including a signal line that transmits an electric signal which is amplified by the amplifier transistor, control signal lines that drives the above-mentioned transistors, a power-supply line, and so forth run, and the wiring lines prevent light from reaching the photodiode.
In contrast, in a CCD image sensor, each pixel includes, not only a photodiode region, but also a vertical CCD transfer region for transferring charge which is obtained by photoelectric conversion. Because a false signal is generated when light enters this region, the region must be blocked from light.
As described above, a light-blocking region is formed in a unit pixel in an image sensor.
Accordingly, in an image sensor of the relate art, a technique is proposed and put into practical use, in which a microlens and an in-layer lens are formed above a photodiode for each pixel in order to efficiently collect light onto the photodiode while preventing light from entering a light-blocking region that is formed in the pixel.
However, in this case, the angle of the main light ray that enters a photodiode is typically 0° in a pixel that is provided in the central portion of an image-pickup region (a pixel-array section), and the light perpendicularly enters the photodiode. In contrast, generally, the main light ray enters a photodiode at a certain angle in a pixel that is provided in the peripheral portion of the image-pickup region. Specifically, generally, the main light ray for a pixel that is provided in the peripheral portion of the image-pickup region enters a photodiode with an inclination in a direction away from the central portion of the image-pickup region.
As a result, in the central portion of the image-pickup region, matching of the center of the aperture of a photodiode to the center of a microlens and an in-layer lens is performed. However, in the peripheral portion of the image-pickup region, when matching of the center of the aperture of a photodiode to the center of a microlens and an in-layer lens is performed, an optical axis is inclined with respect to inclined incident light, and one portion of the incident light enters the outside of the photodiode, resulting in occurrence of a shading phenomenon.
Hence, in order to deal with this phenomenon, a technique is proposed and put into practical use, in which a microlens, a color filter, and an in-layer lens are arranged in the peripheral portion of the image-pickup region in such a manner that the position thereof is shifted by an offset in a direction to the center side of the image-pickup region so that the position can be suitable for the optical axis of incident light, thereby avoiding shading that occurs in a photodiode (for example, see Japanese Unexamined Patent Application Publication No. 11-186530). This technique is called a pupil correction technique, and is applied to a wiring line, a contact, a via, and so forth.
In this case, if the wiring line, the microlens, and so forth in a layout in the peripheral potion of the image-pickup region are moved parallel, the layout in the peripheral potion of the image-pickup region coincides with a layout in the central portion of the image-pickup region.
However, in a case in which the above-described pupil correction technique is performed, regarding a microlens and an in-layer lens, because a shift amount by which the microlens and the in-layer lens are to be shifted by pupil correction is not limited, optimization can be easily performed. However, regarding a wiring line, limitations are imposed on a shift amount of the wiring line in accordance with the arrangement of elements in a pixel, the shape of the aperture of a photodiode or the like.
Hence, as a specific example of these limitations, a pixel using a three-layer metal-wiring structure is described as an example. FIG. 6 is a schematic plan view showing an arrangement of elements in the vicinity of an FD unit in a case of three-layer metal wiring.
In the figure, in each pixel, a vertical signal line that transmits, as an electric signal, a signal which is obtained by photoelectrical conversion, and an internal wiring line 114 that connects an FD unit 112 to the gate (not illustrated) of an amplifier transistor are formed commonly using a wiring film that is a second layer. In addition, a contact unit 116 connects the FD unit 112 and the internal wiring line 114.
Note that a wiring line that both blocks light and serves as a power-supply line is formed, as a metal wiring film that is a third layer, on the wiring lines that are illustrated.
In this wiring structure, when the vertical signal line 110 is moved and used for pupil correction, the vertical signal line 110 can be relatively freely moved in a direction away from the contact unit 116 (i.e., the right direction (indicated by the arrow A) shown in the figure). However, regarding the opposite direction (i.e., the left direction (indicated by the arrow B) shown in figure), because the position of the contact unit 116, which connects the FD unit 112 to the internal wiring line 114, cannot be moved, when the vertical signal line 110 is moved by a large amount, the vertical signal line 110 comes into contact with the contact unit. Accordingly, it is impossible to move the vertical signal line 110 with a sufficient flexibility.
Thus, for example, when a pixel is to be miniaturized in a state in which there is no advance of a process generation and in which design rules are not changed, supposing that the number of wiring lines which are to be mounted in a unit pixel is not decreased, a maximum movement amount (a pupil-correction amount) by which a wiring line can be shifted by pupil correction is determined under layout constraints. When the pupil-correction amount of a wiring line is smaller than a pupil-correction amount of a wiring line that is obtained using simulation or theoretical calculation, pupil correction is not sufficiently performed on a wiring line in the peripheral portion of the image-pickup region. Shading that is caused by the wiring line occurs, and sensitivity is decreased.
Furthermore, when a light ray that is generated due to shading leaks into adjacent pixels because of a reflection or refraction phenomenon, degradation in image quality which is called color mixture occurs.
Hence, the present invention aims to provide a solid-state image-pickup device that can perform pupil correction on wiring lines with a high flexibility by improving an arrangement structure of wiring layers.